plugin support

while I was playing with grunt, I realized that we were not so far away from being able to do the plugins things

So here is a plugin design, based on the entry_points apps that was already there, and some require.js tricks.
I did verify the apps are compatible between each combination of grunt prod / grunt dev.
You can do reload server on either of the apps (but not both)
configuration is passed from master.cfg to the apps:

c['www'] = dict(port=8020,
                plugins=dict(sample_plugin=dict(rotate_speed=8)))